Superdiffraction emitting, i.e. far-field spot compression without energy loss in main lob, in space laser communication can increase the main lob energy density. A smaller far-field spot in conjunction with a higher main lob energy density can improve the detection accuracy greatly, and enhance the communication capability of space laser communication system as a result. So superdiffraction emitting is of great significance to space laser communication. In most of the spot compression approaches, the main lob will suffer considerable loss of energy caused by the compression. Aiming at the superdiffraction emitting in space laser communication, we propose two schemes to obtain far-field spot compression without energy loss in main lob. One scheme is based on SA algorithm. We first design the intensity distribution in the far-field receiving plane to meet the particular requirement of space laser communication. According to the desired intensity distribution, we obtain the phase profile of the diffractive phase element (DPE) using the SA algorithm. Placing the designed DPE on the emitting plane, the superdiffraction emitting is achieved. The other scheme is based on YG algorithm. By using the algorithm, we convert the Gaussian beam into an appropriately designed high quality uniform beam in emitting plane. Using the high quality uniform beam as the emitting beam, we then gain far-field spot compression without energy loss in main lob. By means of the two schemes we proposed, the superdiffracion emitting in space laser communication is obtained.
Cooperating with the free-space laser communication terminals, the satellite trajectory simulator is used to test the acquisition, pointing, tracking and communicating performances of the terminals. So the satellite trajectory simulator plays an important role in terminal ground test and verification. Using the double-prism, Sun etc in our group designed a satellite trajectory simulator. In this paper, a high precision dual feedback discrete control system designed for the simulator is given and a digital fabrication of the simulator is made correspondingly. In the dual feedback discrete control system, Proportional- Integral controller is used in velocity feedback loop and Proportional- Integral- Derivative controller is used in position feedback loop. In the controller design, simplex method is introduced and an improvement to the method is made. According to the transfer function of the control system in Z domain, the digital fabrication of the simulator is given when it is exposed to mechanism error and moment disturbance. Typically, when the mechanism error is 100urad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.49urad, 6.12urad, 4.56urad, 4.09urad respectively. When the moment disturbance is 0.1rad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.26urad, 0.22urad, 0.16urad, 0.15urad respectively. The digital fabrication results demonstrate that the dual feedback discrete control system designed for the simulator can achieve the anticipated high precision performance.